Electronic equipment includes groupings of electronic circuits and components that are designed to provide one or more complex functions. The electronic equipment receives power from an energy source that is used to power its electronic circuits and components. The power that is received is input to a power system of the electronic equipment that provides voltage outputs that are delivered to a plurality of loads. The power system often includes one or more voltage regulators that operate in parallel.
Voltage regulators are used to regulate the power that is delivered to one or more circuit cards such that voltage and current stresses on components that reside on a circuit card are reduced. They are used to convert an input voltage that is received from a given energy source to an output voltage that falls within a voltage range that is suitable for the components that reside on the circuit cards. By using a voltage regulator in the power system of electronics equipment, the power density of associated backplanes and line cards can be increased. Voltage regulators that provide a buck-boost function can be a combination of buck and boost converters, or can be a buck-boost converter. Voltage regulator types can include isolated voltage regulators and non-isolated voltage regulators. Because isolated voltage regulators are more complex and less efficient than are non-isolated voltage regulators that have the same power and voltage ratings, it is advantageous to use non-isolated voltage regulators in power systems.
When multiple voltage regulators are connected in parallel, satisfactory current sharing between respective parallel connected voltage regulators should be maintained for proper operation. Usually, the purpose of assuring satisfactory current sharing is to cause each voltage regulator of multiple voltage regulators to output about the same power, i.e. have about the same output current. However, unlike in an isolated voltage regulator, in a non-isolated voltage regulator, when multiple voltage regulators are coupled in parallel, the current flowing in its positive input lead and the current flowing in its negative input lead are not necessarily the same. This is because the input power leads to respective voltage regulators of a complex power system might not have the same voltage or resistance. This also applies to the current flowing in the output leads of a non-isolated voltage regulator.
Conventional power sharing methodologies alone cannot guarantee that during operation the positive and negative input and output power leads of non-isolated voltage regulators will have the same amount of current. However, a power lead of a voltage regulator can be damaged if it carries significantly more current than its counterpart. Because input power leads are usually longer than output power leads in actual power systems, unsatisfactory current sharing is more problematic for input power leads. For safe operation it is desirable to maintain a satisfactory current balance between the positive input lead and the negative input lead of each voltage regulator.
In power systems that include a plurality of voltage regulators that have current sharing control, current balance between the positive and negative input power leads is required. Conventionally, such current balance is maintained by adjusting the gate drive voltage of a switch that is located in the positive or the negative power path of a voltage regulator such that the total resistance in that path is basically equal among parallel connected voltage regulators. However, this approach can result in an unsatisfactorily high power loss in the switch.